1. Field of the Invention
The present invention relates to an electron source with an electrode structure which reduces discharges as well as to an image display apparatus which uses the electron source.
2. Description of the Related Art
Conventional uses of electron-emitting devices include image display apparatus. For example, an evacuated flat electron beam display panel in which an electron source substrate and counter substrate are placed opposite each other in parallel is known, where the electron source substrate contains a large number of cold-cathode electron-emitting devices and the counter substrate is equipped with an anode electrode which accelerates electrons emitted from the electron-emitting devices and phosphor which acts as a light emitting member. The flat electron beam display panel can have lighter weight and larger screen size than cathode ray tube (CRT) display apparatus widely used today. Also, it can provide brighter, higher-quality images than other flat display panels such as flat liquid crystal display panels, plasma displays, and electroluminescent displays.
Thus, for image display apparatus which apply voltage between the anode electrode and cold-cathode electron-emitting devices to accelerate the electrons emitted from the cold-cathode electron-emitting devices, it is advantageous to apply a high voltage to maximize emission brightness. Emitted electron beams are dispersed before reaching the anode electrode depending on the type of device, and thus, to implement a high-resolution display, it is preferable to reduce inter-substrate distance between rear plate and face plate.
However, a shorter inter-substrate distance essentially results in a higher electric field between the substrates, making the electron-emitting devices more susceptible to breakage due to discharges. Japanese Patent Application Laid-Open No. H09-298030 discloses an image display apparatus which places an overcurrent protective member of a low melting-point material between a conductive film equipped with an electron-emitting area and device electrodes and thereby prevents impacts on other devices in case of a short circuit between device electrodes. Japanese Patent Application Laid-Open No. H09-245689 discloses an image display apparatus which places a fuse outside an active area. Japanese Patent Application Laid-Open No. H07-94076 discloses an idea of installing a resistive layer which is burnt out by a short-circuit current, to provide against an emitter-gate short circuit in an FED. It also discloses that by covering the resistive layer with an insulating layer, it is possible to prevent gas generation in case the resistive layer melts, and thereby prevent secondary discharges caused by gas.
However, the techniques disclosed in Japanese Patent Application Laid-Open No. H09-298030, Japanese Patent Application Laid-Open No. H09-245689 and Japanese Patent Application Laid-Open No. H07-94076 are not sufficient and there has been a demand for a method which can prevent the impact of discharges more reliably. If voltage applied to an image forming member is set at a high level, fuses burnt out by discharges can sometimes cause new discharges to be generated, resulting in discharging of large current for an extended period of time. This increases damage and fatally contaminates a vacuum atmosphere in the panel, posing a serious problem to device reliability.